This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. So far only precursors of secreted lysosomal enzymes have been reported on (Kollmann K et al. Proteomics 2005, 15:3966-78;Sleat DE et al. Biochim Biophys Acta 2007, 1774:368-72;Sleat DE et al. J Proteome Res 2008, 7:3010-21;Jaquinod SK et al. Methods Mol Biol 2008, 432:243-58). Our experience with lysosomal proteomics has been documented in Schroeder B et al. Traffic 2007, 8:1676-86. In this project, lysosomal matrix protein will be prepared by fractionation of human placental tissue homogenate. Its quality will be examined by 2D electrophoresis and Western blotting using several antisera against lysosomal matrix proteins. A proteolytic processing lysosomal enzyme precursors occurs in the acidic lumen of endosomes and lysosomes. This is typical for the soluble lysosomal proteins, however, systematic data on the results of the cleavage and /or trimming of the termini are not available. The main goals of the project are: 1. to define the terminal peptides by performing proteomics analysis, and 2. to detect possible heterogeneity of the termini that may result from gradual trimming, perhaps a prelude to the degradation of the lysosomal proteins themselves. As a reference a less enriched sample will be considered. The results are of interest from the point of view of lysosomal pathology also. Lysosomal storage diseases are known to affect the lysosomal proteome quantitatively. Eventually,it will be of interest to explore qualitative changes that may result from an altered processing due to the storage.